08-17-2017, 12:37 AM
Wireless Telemetry for Electronic Pill Technology
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Abstract
This work will address the challenges to facilitate the
development of a high capacity radio system for a small,
miniaturized electronic pill device that can be swallowable or
implant able in human body in order to detect biological signals
or capture images that could eventually be used for diagnostic
and therapeutic purposes. In addition to reviewing and
discussing the recent attempts in electronic pill technology, a
wideband (UWB) telemetry system aimed for the development
of an electronic pill will be presented in this paper. We have
successfully realized more than half a meter UWB page link under
conditions emulating an implant
I. INTRODUCTION
Recent development in electronic pill technology requires
the integration of more complex systems on the same platform
when compared to conventional implantable systems. A small
Fig. 1. A wireless endoscope monitoring system. miniaturized electronic pill can reach areas such as small
intestine and deliver real time video images wirelessly to an
electronic pill technology, a wideband telemetry system aimed external console. Fig. 1 shows a wireless endoscope (i.e. for the development of an electronic pill will be presented in
electronic pill) for a medical monitoring system. The device this paper. We have successfully realized travels through the digestive system to collect image data and more than half a
meter UWB page link under conditions emulating an implant
transfers them to a nearby computer for display with a
distance 1 meter or more . A high resolution video based capsule endoscope produces a large amount of data, which
II. W IRELESS TELEMETRIES USED IN ELETR ONIC PILL
should be delivered over a high capacity wireless link. There are plenty of publications describing the current
Since its early development [1]-[3], wireless endoscope (i.e. trend on wireless endoscopes and technologies. One of the
electronic pill) designs have been based on narrow band recent articles given in [7] gives a good history of capsules
transmission and thus have limited number of camera pixels. from their early development to clinical implementation. The
One of current state-of-the-art technologies for wireless design of wireless capsules started around 1950s. Since then,
endoscope device is commercially available by the company they have been called as endoradiosondes, capsule, smartpill,
Given Imaging [4]. The pill uses the Zarlink s RF chip [5] electronic pill, wireless capsule, wireless endoscopy, video
for wireless transmission based on the Medical Implant capsule and so forth. Herein we will use the term electronic Communication Service (MICS) band. The allowable channel
bandwidth for this band is only 300 kHz. It is difficult to pill to cover all these names. The early attempts were based
assign enough data rate for the high quality video data at the on low frequencies and with simple structures [1][6]. A basic
moment for a real time monitoring. It is quite obvious that transmitter using Collpitts or Hartley oscillator topology
there is a need for higher-bandwidth data transmission for connected to a sensor has been used to send the signal from
electronic pills that could facilitate a better diagnosis. inside the body to external devices for tracking physiological
Wideband technology- (UWB communication) is an ideal parameters of inner organs. Despite simplicity, the early
physical layer solution that achieves a data rate equal or higher systems were bulky due to large electronic components and
than 100 Mbps. Its current applications are mostly for in-door batteries used and were targeting temperature, pH and
entertainment, radar and imaging. Due to high losses in body pressure [8][9].
tissue at high frequencies many are skeptical about using As the electronic device should deeply be placed inside
UWB for implanted and, moreover, ingested devices. This the body, which makes the wireless communication
challenge can only be addressed by combined design of interesting due to its surrounding medium, the recent attempts
antennas, transmitters and receivers as described in this paper. in electronic pills have also been limited to low frequency
In addition to reviewing and discussing the recent attempts in transmissions (UHF-433 ISM or lower) [10]-[16]. The low
[1]
TABLE I. RE CE N T RE S E ARCH PRO JE CT OU T COM E S EOL NE CT RO N ICP IL L.
References
Image Image Frequen. Data Modu- Trans. Physical Power Current
Resolution sensor Rate lation Power Dimension Supply Power
NA
(Thone, 640 X 480 2009)[14] pixels MT9V013 144 MHz 2 Mbps FSK -18 dBm Not finalized 3 V (2 mW for
(VGA) coin cell Tx)
2X 1.5 V
307,200 VGA, 8 mA (24
(Chen, 2009) FSK NA 11.3X26.7 silver[
10] pixels 0-2 fps 433 MHz 267 kbps mmxmm oxide mW)
( Wang, 510X480 PO1200 10x190 3 V, NA NA AM High
2008) [13] pixels (variable) mmxmm wireless 125 mW CMOS
(Kfouri, 768 X 494 CCD Li-ion
2007)[16] pixels ICX228AL UHF 250 kbps -- NA 20X100
mmxmm battery --
(Park, 2002) 510X492 OV7910 AM NA 10 X 7
[13] pixels CMOS 315 MHZ NA mmxmm 5 V NA
2X1.5 V
Johannessen, Sensory: pH OOK NA, 1m 12X36 SR48 15.5 mW
2006) [11] pH and Temp. and Temp. 433 MHz 4 kbps mm, 8g
Ag2O
Valdastri, 27X19X19 3-V Sensors 433 MHz 13 kbps ASK 5.6 mW coin cell
2004 [12] Multi-channel mm 3 5 m (CR1025) --
Mackay, pH, temp., Sensors 100 kHz -- FM - -- -- -- 1957 [1] oxygen level
The highlighted section is for visual based electronic pill systems.
frequency transmission is easy to design and is found data rate are desired for the purpose of low-power
attractive due to its high efficiency. However a low frequency consumption and miniaturization.
link requires large electronic components such as capacitors Another type of capsule is the robotic endoscope [13]
and inductors, which makes it difficult to realize a complete which additionally has features such as locomotion and the
integrated system. energy transmission using electromagnetic coupling.
After recent significant technology improvements, design Although the device size is quite large comparing to other
of small size camera and battery could have been possible. proposed systems, it is probably because of these additional
Thus in the last ten years some research projects looking at functionalities. Similar to smartpill, such a device can be
developing electronic pills have concentrated mostly on the used for precise drug delivery in the human gastrointestinal
visual sensor system. Thus a high frequency page link is required tract. Real-time energy transfer is necessary for these types of
for better resolution and a miniaturized system. Recent endoscopes to provide mechanical function as they require
telemetry systems being developed for the electronic pill large power for continuous movement.
technology are summarized in Table I. All these systems are A recent study [14] demonstrated a prototyping system to
still at prototype levels. achieve high data rate (2 Mbps) for higher image resolution.
In [10], a wireless endoscope system uses a commercial It can enable an image resolution up-to 15-20 fps (frame per
RF transceiver operating at 433 MHZ ISM with 267 kbps. second) using compression technique like JPEG. It uses a
The electronic pill includes a passive wireless page link used for simple Colpitts oscillator. The transmitter itself thus
wake-up to reduce power consumption. The wake-up system consumes low-power. However the actual power
recovers energy from a 915 MHz RF modulated signal with consumption of a device could only be realistic when all
some sort of identification code. This capsule does image blocks of an electronic pill are integrated together. The device
compressing techniques using an ASIC to enable higher operates at 144 MHz, relatively lower than most of the
transmission rate of images for low data rate systems. systems that are operating at UHF, which necessitates a larger
The pill in [11] uses a simple OOK wireless system. antenna that will increase the physical size. In [15], Park, et
Similar to the early developments, this device transfers the al . also uses a simple AM (amplitude modulation). It is
physiological data- pH and temperature. Another such device designed with a mixer and an oscillator circuit together with
was developed by Valdastri, et al., in [12] with a multi- the CMOS image sensor and a loop antenna to form a
channel feature to cover few different physiological capsule-shaped telemetry device. This device uses an external
parameters. It was tested in vivo in pigs using pressure control unit to control the capsule inside the human body.
sensors. The transmission range was reported as 5 m. These Another category of electronic pill technology is to use
devices do not require high data rate comparing to the video fluorescence spectroscopy and imaging, similar to those that
based electronic pills highlighted in Table I because are commercially available. Kfouri, et al., studied a
physiological parameters like pH and temperature are low- fluorescence-based electronic pill system that uses UV light
frequency signals. Simple modulation schemes like On-Off with illumination LEDs to obtain clearer images [16]. This is
Keying (OOK) and Amplitude Shift Keying (ASK) with low- like flash based digital camera widely used by people. Due to
[2]
the use of power hungry LEDS, such a device consumes from the Food and Drug Administration (FDA). The device
power higher than the other available systems. An alternative contains 6 LEDs with adjustable illumination to maintain
power source together with battery is required to support the optimal imaging. Currently all the video based commercial
electronics continuously. A wireless power, from outside to systems being designed are based on illumination. The
electronic pill by SmartPill is designed to inside, has been suggested. Although not specified, it measure pressure,
probably used UHF frequency as the RF transmission. pH and temperature as it passes through the GI tract. A
From T able I, it seems that in current attempts the receiving device worn by the patient collects data which is
transmission frequency has been limited to around UHF later examined by a physician. With information obtained
frequencies. Although the advances in high frequency and from public domain, these pills are described in Table II.
high bandwidth communication technologies for wireless Due to the limited transmission bandwidth used for the
systems have been significant in the commercial domain, electronic pills that are currently being developed or the ones
these technologies are not directly transferable to biomedical commercially available, the image transfer rate has been
implant or ingested systems due to the differing power, size, limited to 0-10 frames per second. As high definition cameras
and safety related radiation requirements. As an example, in are continuously being developed, they will be attractive for
[17] an implant prototyped with a ZigBee compliance one of use in electronic pill. However, a higher pixel camera will
the low-power, less complex and small size commercially available wireless standard occupies an area of 26X14X7 mm 3 require higher image transfer rate. As an example, if 1920 x
without being integrated with other required blocks of an 1080 pixel (2 megapixel) charge-coupled device (CCD)
electronic pill. The existing advanced wireless systems such as sensors to be integrated in an electronic pill, it will require a
ZigBee (IEE 802.15.4), WLANs, and Bluetooth (IEE data rate of 33.2 Mbit/frame, considering 2 Bytes are used per
802.15.1) operate at 2.4 GHz ISM band and suffer from the frame. Currently such a high data rate is not possible with any
strong interference from each other when located in the same of the available telemetry systems in electronic pills. If the
environment [18]. Thus an electronic pill should probably allowable bandwidth used with UHF frequencies, transmission
have a different transmission band for an interference free of this data rate will only give a transmission time of 10s or
wireless system. The existing wireless modules contain more per frame which will result in very small motion for a
complex multi-access communication protocols such as video streaming. Although compression techniques could be
OFDMA that increase the power consumption and size of the used to some extend, it reduces the image equality. Thus in
wireless chip. Unless these chips are miniaturized to levels future, a dedicated frequency band with larger bandwidth is
that can be inserted into a capsule size of 11mmX30 mm, the required for high definition image transmission.
telemetry used will still be based on simple communication Since miniaturization is important, different design
modulations like ASK, OOK, FSK, AM. approaches have been followed by the designers. Fig. 2
Table II summarizes the commercially available electronic illustrates different shapes that has been used or can be used
pill technologies that are already been used in clinical to integrate all the necessary blocks. As shown, each unit can
environments. Current wireless endoscope device by Given be designed on a separate board layer and then stacked on top
Imaging is used to diagnose disorders such as Crohn's of each other. In a design shown in Fig. 2-(a) antenna can be
disease, Celiac disease, benign and cancerous tumors, placed such that it can easily be inserted on top of the ulcerative colitis, gastrointestinal reflux disease (GERD), and
Barrett's esophagus [4]. The pill uses the Zarlink s RF chip for transmitter layer. The capsule shape is also divided into two
wireless transmission [5]. The chip uses the MICS band that regions where antenna can be designed to be placed in upperallows
channels with only 300 kHz. It is thus difficult to half whereas the remaining electronic units are packed in the
assign enough data rate for the high quality image and video lower-half. Placing electronic units on one side of antenna is
data at the moment for a real time data transfer and another possibility (Fig. 2-©). Commercially available mini
monitoring. cameras can easily be integrated with electronic pills [19].
RF Norika by RF system lab has a wireless power Small miniature rechargeable battery technologies are also
capability and localization capabilities. Another endoscope being developed [20] with a dimension around 5 mm and can
EndoCapsule was developed by Olympus was mainly used in easily be integrated in a capsule structure shown in Fig. 2.
Europe. However in 2007 it has received marketing clearance
TABLE II. CO MP ARIS ON OFHAR DW A RE DE SIG N S FRO MVEN D ORS , givenimaging.com , http://olympus-europaendoscopy/ ,
rfsystemlab.com , smartpillcorp.com .
Model Company camera
Model Company Camera
Freq. Data Power Physical Image rate and
(Sensor) (MHz) Rate Source Dimension resolution
PillCam (SB) Given 402-405 800 14 images per
Micron, CMOS & 433 kbps Battery 11X26 Imaging (Zarlink) mmxmm, <4 gr second, or 2,600 (FSK)
color images
EndoCapsule Olympus CCD camera, 2 images per
Optical 1920 X 1080 -- -- Battery 11X26
mmxmm second
Norika RF System CCD Image 9X 23
Lab sensor - -- Wireless Power mmxmm NA
SmartPill Smartpill acidity (pH), Only sensor
Corp. press., temp. -- -- Battery 13X26
[3]
mmxmm discrete data
printed antenna presented herein demonstrates good matching
in the frequency band of 3.5-4.5GHz and the radiation
performance has been evaluated experimentally using the IUWB
transmitter/receiver prototype to show that it is suitable
for an electronic pill. The antenna matching has been
optimized using CST Microwave Studio, commercial
electromagnetic simulation software. Proposed antenna is
printed on a 0.5mm thick RO4003 capsule-shaped, low loss,
dielectric substrate ( e = 3.38 ). It can easily fit inside a
r
size-13 capsule. Overall length and width of the antenna is
28.7mm and 14mm, respectively. The antenna has been
Fig. 2. Possible physical shapes for electronic pills optimized using simulations and printed on one side of the
substrate together with a Grounded-CPW (Coplanar Wave
II. IW-UWB TELEMETRY FOR ELECTRONIC PILL
(Guide) feed as shown in Fig. 4.
Several transmitters have been designed to generate UWB
Although the image based electronic pill systems listed in signals. Short pulses are mainly generated according to the
Table I & II can provide some level of accuracy, for some OOK and Pulse Position Modulation (PPM) modulated signal.
diseases detailed images may be required [21]. Thus a better At the transmitter, the pulse generator unit produces a
resolution camera will be used. In order to monitor high rectangular- shaped pulse with 1ns width (Fig. 3-(a)). The
quality images in real-time, a wideband radio page link will be spectrum of the rectangular pulse extends over an unlimited
desired for a high capacity data transfer and thus improved frequency band. Thus a Band Pass Filter (BPF) centered at 4
image resolution [14][22]. A wideband, high frequency GHz with 1 GHz bandwidth is used to constrain the signal
technology will especially be useful for high definition images power under the Federal Communications Commission (FCC)
exceeding 2 megapixels (i.e. > 1920 x 1080). Although there emission mask (i.e. a band limited UWB system). The energy
have been ongoing advancements in UWB communication for of the side lobes is maximized within the bandwidth of the
short range applications; they cannot directly be applied to bandpass filter. The filtered pulses are fed into our custom
electronic pill technology because of different design and made UWB antennas, shown in Fig. 3 and 4.
optimizations required due to stringent physical constraints The receiver can easily be designed for a high data rate as
and biological safety. In the following section, we will study it is built from off-the-shelf high performance RF components
the feasibility of wideband technology for electronic pills. by using high performance RF ICs (i.e. Amplifiers, Mixers)
The important parameters of the wideband technology are and high speed Field Programmable Gate Arrays (FPGA).
its low power transmitter design, low-interference effect in There are different receiver architectures that can easily be
medical environment and high data rate capability. The design constructed. Usually a mixer is used to down convert the high
of a UWB wireless chip has been difficult for chip designers frequencies to low frequencies. Herein a diode is used due to
due to the difficulty in the demodulation of narrow pulses with simplification in the successive blocks. T he received UWB
a low signal power level. Generally a UWB receiver circuit signal is passed through a BPF, whose center frequency is 4
has demonstrated power consumption higher than that of a GHz, to eliminate possible interference from the frequencies
narrow band system. One way to eliminate the high power of WLAN standards (for example 2.4 GHz and 5 GHz). The
consumption of an ultra wideband transceiver is to use a signal is then amplified by the Low Noise Amplifier (LNA). A
transmitter only in the electronic pill that will not need a signal diode and a Low Pass Filter (LPF) down converts the UWB
from external unit to the electronic pill in the body. signal and the baseband data is finally recovered by the
The use of wideband technology for medical implants FGPA. At the receiver end, the main component is the diode
should overcome unique challenges associated with the high detector. When small input signals below -20dBm are applied
frequency implementation. To address these challenges, as to the diode, it translates the high frequency components to
preliminary work in this study, we present a complete their equivalent low frequency counterparts due to its
nonlinear characteristic. Measurement results, shown in Fig. working UWB prototype with a capsule-shaped antenna 3(b) are spectrum plots at the outputs of the receive antenna
specifically designed for the targeted application. The and the low-noise amplifiers.
selected band is 3.5-4.5GHz (i.e. band-limited), which avoids UWB prototype is capable of supporting a low-power
narrowband systems operating in the ISM bands. The initial UWB communication, which will be ultimately used to form
design has been tested in a laboratory environment an in-body-to-air link, without violating FCC regulations.
demonstrating that an impulse-based UWB system is an Antennas were placed inside a plastic container. Prior to each
attractive design for wireless endoscope monitoring. The measurement, jacket of aluminum foil covered the outer
result shows that with UWB signals it is possible to transmit surface of the container to minimize outside coupling paths
data at a rate of 100 Mbps. between the antennas.
The prototype system used in the experiment is shown in First measurement was taken inside the empty container
Fig. 3, with transmitter and receiver waveforms shown and the second with a meat sample inside. Measured S21
explicitly. A low-cost, printed, capsule-shaped UWB antenna using the VNA is shown in Fig. 5. Coupling between antennas
in the same laboratory environment and instrument calibration